1. Field of the Invention
The present invention relates to an anti-reflection coating (ARC) layer and a design method thereof. More particularly, it relates to an anti-reflection coating layer with a substrate reflectivity substantially equal to zero, and a design method thereof.
2. Description of the Related Art
As line width is reduced in semiconductor manufacturing process, it is more difficult to perform a photolithographic process. With the shrinkage of line width, misalignments easily occur. Especially during an exposure process, due to the interference of light reflected from under layers and the substrate under a photoresist layer, the photoresist patterns defined may be distorted or deviate, leading to incorrect transfers of the photolithographic pattern.
In order to prevent the misalignment, an anti-reflection coating layer usually is formed under the photoresist layer to reduce the substrate reflectivity. FIG. 1 is a schematic cross-sectional view of an anti-reflection coating layer in a semiconductor of the prior art.
In FIG. 1, the under layer 102 is formed over the substrate 100. The anti-reflection coating layer 104 is then formed over the under layer 102, wherein the anti-reflection coating layer 104 has a refraction constant (n), an extinction coefficient (k) and a thickness. The photoresist layer 106 is then formed over the anti-reflection coating layer 104 in order to perform the exposure process. When the exposure light source 110 is incident to the photoresist layer 106 and reaches the anti-reflection coating layer 104, the anti-reflection coating layer 104 reduces the light incident to the substrate 100. Thus, the substrate reflectivity can be reduced.
The values of n, k and thickness of the anti-reflection coating layer must be adjusted according to the materials used in the under layer 102 and the substrate 100 in order to optimize the anti-reflection of different under layers 102. That is, great efforts must be taken to optimize the n, k and thickness values of the anti-reflection coating layer. Therefore, an all-purpose anti-reflection coating layer applicable to different under layers and a design method thereof are desired.